1. Field of the Invention
The present invention relates to a liquid droplet ejection apparatus for ejecting droplets of liquid, such as liquid material or fluid, from an ejection opening through pressurization of the liquid within a pressurizing chamber.
2. Description of the Related Art
The liquid droplet ejection apparatus of this type includes a pressurizing chamber into which liquid is introduced via a liquid introduction bore, an ejection nozzle communicating with the pressurizing chamber, and pressurizing means, such as a piezoelectric/electrostrictive element, for changing the volume of the pressurizing chamber. The apparatus pressurizes liquid contained in the pressurizing chamber through change in the volume of the pressurizing chamber to thereby eject the liquid in the form of droplets from an ejection opening of the ejection nozzle. Such a liquid droplet ejection apparatus is used in, for example, a color printer.
However, since a conventional liquid droplet ejection apparatus is intended to eject merely a single droplet of liquid by a single operation of pressurization, the diameter of a liquid droplet is relatively large. Thus, the conventional apparatus cannot be used in mechanical equipment requiring mistlike fuel or the like.
An object of the present invention is to provide a liquid droplet ejection apparatus capable of ejecting liquid in a mistlike form.
To achieve the object, the present invention provides a liquid droplet ejection apparatus comprising a pressurizing chamber communicating with a liquid supply path via a liquid introduction bore; an ejection nozzle connected to the pressurizing chamber; and a piezoelectric/electrostrictive element for changing a volume of the pressurizing chamber so as to pressurize liquid introduced into the pressurizing chamber via the liquid introduction bore to thereby eject the liquid in a form of liquid droplets from a circular ejection opening of the ejection nozzle, wherein a diameter of a largest liquid droplet among the liquid droplets ejected is not greater than a diameter of the ejection opening.
Also, the present invention provides a similar liquid droplet ejection apparatus configured such that a plurality of liquid droplets are simultaneously ejected from the ejection opening by means of a single operation of pressurization.
Furthermore, the present invention provides a similar liquid droplet ejection apparatus configured such that a plurality of liquid droplets ejected from the ejection opening by means of a single operation of pressurization simultaneously reach an imaginary plane defined in a manner such that all points on the plane maintain an equal distance to the ejection opening.
These liquid droplet ejection apparatuses can be used in mechanical equipment requiring mistlike fuel or the like (e.g., a gasoline-injection-type internal combustion engine) and eject (inject) liquid through effective utilization of a piezoelectric/electrostrictive element.
Preferably, any one of the liquid droplet ejection apparatuses described above is configured such that each of the liquid introduction bore and an ejection-side end portion of the ejection nozzle assumes a hollow, substantially cylindrical form, and a bottom face of the cylinder forming the ejection-side end portion of the ejection nozzle serves as the ejection opening; the ratio of the diameter of the liquid introduction bore to the diameter of the ejection opening is 0.6 to 1.6; the ratio of the diameter of the ejection opening to the height of the hollow cylinder forming the ejection-side end portion is 0.2 to 4; and the rate of change (per unit time) in the ratio of the amount of change in the volume of the pressurizing chamber to the sum of the volume of the ejection nozzle and the volume of the pressurizing chamber is 6 ppm/xcexcs to 40 ppm/xcexcs.
The ratio of the diameter d0 of the liquid introduction bore to the diameter d1 of the ejection opening (d0/d1) is 0.6 to 1.6 for the following reason. When the ratio (d0/d1) is less than 0.6, the amount of liquid to be introduced into the pressurizing chamber via the liquid introduction bore becomes small in relation to the amount of liquid to be ejected from the ejection opening, causing an ejection defect. When the ratio (d0/d1) is in excess of 1.6, during pressurization, a large amount of liquid flows back into the liquid supply path from the pressurizing chamber via the liquid introduction bore, resulting in a failure to eject liquid from the ejection opening.
The ratio of the diameter d1 of the ejection opening (i.e., the diameter d1 of the bottom face of the hollow cylinder) to the height h1 of the hollow cylinder formed at the ejection-side end portion (d1/h1) is 0.2 to 4 for the following reason. When the ratio (d1/h1) is not greater than 4, during ejection, contact resistance between liquid and the inside wall surface of the ejection-side end portion becomes relatively large, so that vibration remaining, on liquid surface, immediately after ejection settles promptly, thereby preventing air (a bubble) from being caught in the ejection nozzle. As a result, entry of a bubble into the pressurizing chamber from the ejection nozzle can be prevented, thereby enhancing ejection stability. When the ratio (d1/h1) is less than 0.2, during ejection, contact resistance between liquid and the inside wall surface of the ejection-side end portion becomes excessively large. As a result, the force of ejection becomes insufficient, resulting in disabled ejection.
The rate of change (per unit time) R in the ratio of the amount of change xcex94V in the volume of the pressurizing chamber to the sum of the volume xcex94n of the ejection nozzle and the volume Vk of the pressurizing chamber (xcex94V/(Vn+Vk)) is 6 ppm/xcexcs to 40 ppm/xcexcs for the following reason. The greater the rate of change R, the smaller liquid droplets become. However, when the rate of change R is in excess of 40 ppm/xcexcs, ejection becomes unstable. When the rate of change R is less than 6 ppm/xcexcs, droplets to be ejected become granular. As a result, an object that a plurality of liquid droplets are ejected by means of a single operation of pressurization cannot be attained.
Preferably, any one of the liquid droplet ejection apparatuses described above is configured such that an ejection-side end portion of the ejection nozzle assumes a hollow, substantially cylindrical form and is formed such that a bottom face of the cylinder serves as the ejection opening; and an inside diameter of the cylinder increases toward the ejection opening. In this case, preferably, a value obtained by dividing, by the height h1 of the cylinder, the difference between the diameter d1 of the bottom face of the cylinder and the diameter d2 of the top face of the cylinder serving as an opening located on the side of the pressurizing chamber ((d1xe2x88x92d2)/h1) is 0.05 to 0.7.
Through employment of the geometric features mentioned above, the liquid is ejected in a mistlike form for the following reason. Conceivably, during ejection, the liquid is subjected to not only a force imposed along the axial direction of the hollow cylinder (i.e., along the direction perpendicular to a plane serving as the ejection opening), but also a force imposed along a direction perpendicular to the axial direction and exerted from the inside wall surface of the hollow cylinder; thus, the liquid becomes unlikely to assume a large granular form.
Also, any one of the liquid droplet ejection apparatuses described above is preferably configured such that the ejection-side end portion of the ejection nozzle comprises a first ejection bore formed in a thin-plate member and assuming a hollow, substantially cylindrical form having a top face located on the side of the pressurizing chamber and a bottom face located on the side of the ejection opening; and a second ejection bore assuming a hollow, substantially cylindrical form and formed in a liquid-repellent layer formed on the surface of the thin-plate member located on the side of the ejection opening, a top face of the hollow cylinder forming an opening connected to the bottom face of the first ejection bore, a bottom face of the hollow cylinder forming the ejection opening of the ejection nozzle. The inside diameter of the second ejection bore increases toward the ejection opening. In this case, preferably, a value obtained by dividing, by the height of the second ejection bore, the difference between the diameter of the ejection opening of the second ejection bore and the diameter of the opening of the second ejection bore connected to the first ejection bore is 0.5 to 2.0.
The liquid-repellent layer is provided in order to prevent adhesion of liquid droplets to an area around the ejection opening during ejection. When the liquid-repellent layer is provided, the liquid-repellent layer substantially serves as the end portion of the ejection nozzle. Accordingly, when, as mentioned above, the hollow, substantially cylindrical second ejection bore formed in the liquid-repellent layer is configured such that the inside diameter thereof increases toward the ejection opening, the liquid is subjected to not only a force imposed along the axial direction of the second ejection bore (hollow cylinder), but also a force imposed along a direction perpendicular to the axial direction; thus, the liquid becomes unlikely to assume a granular form. As a result, the liquid is ejected in a mistlike form.
Further, preferably, in the above-described liquid droplet ejection apparatus having the first and second ejection bores, the inside diameter of the first ejection bore decreases toward the second ejection bore.
Through employment of the geometric feature that the inside diameter of the first ejection bore decreases toward the second ejection bore, variation in liquid pressure within the pressurizing chamber immediately after ejection becomes unlikely to occur, thereby lowering the possibility of entry of a bubble into the pressurizing chamber from the ejection nozzle. As a result, ejection becomes stable.
Also, any one of the liquid droplet ejection apparatuses described above is preferably configured such that an ejection-side end portion of the ejection nozzle assumes a hollow, substantially cylindrical form and is formed such that a bottom face of the cylinder serves as the ejection opening; and a protrusion portion is formed on an inside wall surface of the ejection-side end portion. In this case, the ratio of the height of the protrusion portion to the diameter of the ejection opening preferably falls within the range of 0.03 to 0.17. Moreover, three to twelve protrusion portions are preferably formed along the inside wall surface of the ejection-side end portion.
The protrusion portions split a liquid droplet immediately before ejection, thereby facilitating ejection of liquid in a mistlike form.
Preferably, in any one of the liquid droplet ejection apparatuses described above, the pressurizing chamber and the ejection nozzle are integrally formed of zirconia ceramics.
By virtue of characteristics of zirconia ceramics, a liquid droplet ejection apparatus having high durability against frequent deformation can be readily manufactured.
Embodiments of the present invention will next be described with reference to drawings. Herein, the term xe2x80x9cpiezoelectric/electrostrictivexe2x80x9d means piezoelectric and/or electrostrictive. The piezoelectric/electrostrictive element is widely known as an element characterized by extending primarily in a direction parallel to an externally applied electric field and contracting in a direction perpendicular to the electric field and adapted to convert electrical energy to mechanical energy and vice versa. A piezoelectric element is characterized by exhibiting coercive electric field (external electric field as observed upon inversion of polarization) of relatively high intensity. An electrostrictive element is characterized by exhibiting coercive electric field of very low intensity.